AUTHOR=Damiani Elisa , Casarotta Erika , Orlando Fiorenza , Carsetti Andrea , Scorcella Claudia , Domizi Roberta , Adrario Erica , Ciucani Silvia , Provinciali Mauro , Donati Abele 

TITLE=Effects of Normoxia, Hyperoxia, and Mild Hypoxia on Macro-Hemodynamics and the Skeletal Muscle Microcirculation in Anesthetised Rats

JOURNAL=Frontiers in Medicine

VOLUME=Volume 8 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2021.672257

DOI=10.3389/fmed.2021.672257

ISSN=2296-858X

ABSTRACT=Objectives: Excessive oxygen (O2) administration may have a negative impact on tissue perfusion by inducing vasoconstriction and oxidative stress. We aimed to evaluate the effects of different inhaled oxygen fractions (FiO2) on macro-hemodynamics and microvascular perfusion in a rat model.
Methods: Isoflurane-anesthetised spontaneously breathing male Wistar rats were equipped with arterial (carotid artery) and venous (jugular vein) catheters and tracheotomy, and randomized into three groups: normoxia (FiO2 21%, n=6), hyperoxia (FiO2 100%, n=6) and mild hypoxia (FiO2 15%, n=6). Euvolemia was maintained by infusing Lactate Ringer solution at 10 ml/kg/h. At hourly intervals for 4 hours we collected measurements of: mean arterial pressure (MAP); stroke volume index (SVI), heart rate (HR), respiratory rate (by means of echocardiography); arterial and venous blood gases; microvascular density and flow quality (by means of sidestream dark field videomicroscopy on the hindlimb skeletal muscle). 
Results: MAP and systemic vascular resistance index increased with hyperoxia and decreased with mild hypoxia (p<0.001 in both cases, two-way analysis of variance). Hyperoxia induced a reduction in SVI, while this was increased in mild hypoxia (p=0.002). The HR increased under hyperoxia (p<0.05 versus normoxia at 3 hours). Cardiax index, as well as systemic O2 delivery, did not significantly vary in the three groups (p=0.546 and p=0.691, respectively). At 4 hours, microvascular vessel surface (i.e., the percentage of tissue surface occupied by vessels) decreased by 29 ± 4% in the hyperoxia group and increased by 19 ± 7 % in mild hypoxia group (p<0.001). Total vessel density and perfused vessel density showed similar tendencies (p=0.003 and p=0.005, respectively). Parameters of flow quality (microvascular flow index, percentage of perfused vessels and flow heterogeneity index) remained stable and similar in the three groups.
Conclusions: Hyperoxia induces vasoconstriction and reduction in skeletal muscle microvascular density, while mild hypoxia has an opposite effect.